The invention relates to a process for the treatment of water, particularly for treating drinking water and for purifying waste water in which, for the oxidation of undesirable substances in the water and for the improvement of the coagulation of such materials, at least a partial flow of the water is treated with ozone.
Ozone is a preferred oxidation agent for the decomposition of undesirable substances in the water. It has to be produced, however, with a high energy cost from air or from pure oxygen before it can react, brought in solution, with the harmful substances in the water. Dissolving the ozone in the water is rather difficult and requires a considerable expense in operating and capital costs. The problems are especially that ozone can only be used, among others for safety reasons, as a mixture with other gases. Normal air-ozone mixtures contain, for example, only one to two percent by weight of ozone. Washing the ozone from such mixtures if very expensive. Better are processes, on the other hand, in which ozone is produced from pure oxygen, since here higher ozone concentrations are attained from the beginning. It is, of course, a disadvantage that the ozone cannot be produced from air, which is available free of charge, but must be prepared from oxygen. Only those processes of this type are economical in operation in which the oxygen contained in the ozone-oxygen mixture is not lost, but can be used again in some form or another. The invention is, therefore, based on such a process type.
Such a process is known from German Preliminary Published Application No. 25 56 328. Ozone is prepared in high concentrations from oxygen in this process. A partial flow of the water to be treated is brought in contact in a packed column with the ozone-oxygen mixture. Almost all the ozone as well as a portion of the oxygen is dissolved in the water. The oxygen which is not dissolved is withdrawn from the column head and again led to the ozonizer.
The partial flow of the waste water highly charged with ozone is withdrawn at the base of the column and mixed with the quantity of water to be treated. The total quantity of water can also be pumped for the purpose of waste water treatment via the column, which is then simultaneously absorption and reaction chamber. The quantity of water which is led via the column is adjusted to the ozone and oxygen need of the total quantity of water to be treated.
Dissolving the ozone in the packed column takes place under pressure whereby the pressure is built up by compressing the gas with a water ring compressor and the work in the column takes place at a low temperature to increase the solubility of the ozone in the water as well as to reduce the nitrogen percentage in the circulation gas to a degree favorable for ozone production. In case the water to be treated is not under a sufficiently high pressure as yet, the water or a partial flow thereof must be brought to the column pressure with a pump.
An equilibrium occurs between the oxygen which is not dissolved in the water and the nitrogen which degases the water in the circulation gas which is again provided to the ozonizer. The equilibrium is regulated, according to the nitrogen saturation degree of the water and according to the resulting partial gas presure, by the column pressure in such a way that optimal operating conditions exist for the ozonizer.
The advantages of the known processes are found in the almost one hundred percent ozone absorption, in the nitrogen reduction in the circulation gas, in the low gas drying costs and in the doubling of the ozone quantity and ozone concentration by the use of oxygen instead of air at the same energy consumption. The lower energy consumption for drying compared to other oxygen and air processes can be explained in that the wet circulation gas has reduced, determined by the higher column pressure, its operating volumn and, therefore, also the water quantity carried along, which must be adsorbed by the drying installation.
Other known processes in which the ozone is brought in solution with turbines, immersed aerators, filter cartridges or injectors do not attain the high degree of ozone absorption as that of the known process of German Preliminary Published Application No. 2,556,328. Nevertheless, this process also has some weak points. They are the high investment cost for the packed column which must be made of V4A steel because of the aggresiveness of the ozone. Sealing and water level control for the water ring compressor are also very expensive. The sealing and rotating parts of the water ring compressor wear out easily.